Small marine craft operating primarily in shallow water are often referred to as mud boats. Such boats are usually shallow draft flat bottom boats powered by in-board air cooled engines with outboard drives adapted to pass through the hull or transom for coupling to the engine, as disclosed by U.S. Pat. Nos. 941,827, 3,752,111 and 4,726,796.
In some cases small air cooled engines have been adapted for fixed attachment to a boat's transom for pivotal steering in the horizontal plane, with an extended drive shaft extending rearwardly to just below the water line at an angle of approximately 30 degrees as illustrated by Foreman in U.S. Pat. No. 6,302,750.
Other patents, such as Carter, et al. in U.S. Des. 259,488 illustrate the use of an air cooled engine pivotally mountable to the boat's transom with the same elongated drive shaft extending to just below the waterline perhaps at a somewhat greater angle, depending on the height of the transom. In most cases the drives are designed not to extend below the bottom of the hull.
Lais et al. and others disclose the use of electric motors in combination with a belt drive to maneuver small craft as is disclosed in U.S. Pat. Nos. 5,336,119 and 1,953,599. Obviously, such drives are not intended for high speed or for extended powering through mud or vegetation in shallow water.
The use of air cooled or water cooled marine engines coupled by belt to a transom mounted drive unit are well known within the art as being a most efficient means for driving a propeller shaft thereby reducing friction and improving mechanical advantage over right angle gear drives. Therefore, the use of a belt drive in combination with an air cooled engines as disclosed by Pignata in U.S. Pat. No. 5,435,763 seems to be an obvious choice. However, Pignata utilizes a unique internal propeller arrangement and with a through the transom coupling for an inboard air-cooled engine with pivotal kick-up capability or over the top of the transom arrangement. However, Pignata fails to fully disclose how either such arrangement may be steered effectively. While the Pignata apparatus may be useful in open water, it is far from obvious that it could be adapted for use in shallow water marsh with heavy mud and vegetation. The internal propeller housing must be located below the boat hull for water to be drawn effectively through the internal propeller blades. Therefore, if the propeller housing were above the bottom of the boat's hull, water flow would be blocked, Shallow draft boats are known to create a depression at speed for some distance directly behind the transom. It is therefore essential that the propeller shaft extend below the boat hull or beyond the water depression to make sufficient contact with the water to provide thrust and prevent cavitations.
Mud boats rely a great deal on propeller contact with the mud and the propeller's ability to cut the vegetation to help drive the boat. Hence the concept of having an elongated drive shaft extending at a shallow angle from above a boat's transom to just below the water surface has long been the excepted practice for mud boats. However, the use of a fixed inboard engine with a through transom coupling limits the apparatus to a particular boat and therefore may not be removed and mounted on another boat without extensive modifications. The use of a removable over the transom mounted air cooled engine with extended drive shaft is awkward and often limited to a relatively low horsepower engines. There is obviously a need to provide a relatively high horsepower air cooled engines adapted to an efficient belt drive for mounting to small, flat bottom boats in much the same manner as water cooled outboard engines. Such a driver must also be equipped with a foot that does not extend below the bottom of the boat but extends a sufficient distance behind the boat to insure the proper angle of attack when the propeller is in contact with mud and vegetation.
The use of a wide variety of commercially available air-cooled engines with 50 horsepower or more presents a wide range of problems that must be addressed and that are not encountered by conventionally manufactured outboard engine manufactures. By not manufacturing the engine, the drive must be adaptable to multiple engine configurations and drive train configurations. The weight of the engines must be considered and balanced in regard to the drive. Unique pivotal adjustments are necessary to insure safety and proper angles of attack at various speeds. The use of transmissions and clutches must also be considered in an attempt to reduce weight and cost. Conventional drives are inadequate due the constant inter-reaction with debris and mud including stumps and rocks. Therefore, consideration must be given to special propellers and their couplings when used as solids conveying means. Contact with underwater objects is a serious safety problem with mud boat drives since the engine can kick up or sideways causing serious harm to the operator.
It should be understood that a distinction should be made between air cooled engines utilizing a fully enclosed, self contained, circulating water system and water cooled marine engines that utilize the water in which they are submersed, for cooling. Some air cooled marine outboard engines have also been developed. However, for the purpose of this application air cooled engines used as an outboard drive are considered to be both air and self-contained water-cooled engines generally used for inboard drive engines or utility applications other than marine.